1. Field of the Invention
The present invention relates to a maintenance unit for an ink jet head that forms images by ejecting ink, and for an ink jet printer.
2. Related Background Art
As shown in FIGS. 4 and 5, a carriage 101 that holds an ink jet head 100 is supported by a guide rail 102 along which the ink jet head 100 can be moved in the main operating direction, and along which the ink jet head 100 can be moved to a predetermined location at an appropriate acceleration and at a predetermined speed. Depending on the functions of and the specifications for an ink jet printer, a plurality of ink jet heads 100 are prepared, and the positions of the ink jet heads 100 and the distances between them are adjusted to within a predetermined range. A platen 110 is arranged, at a position facing the ink jet head 100, so that a constant distance from the ink jet head 100 is maintained, regardless of the position of the carriage 101 in the main operating direction. The platen 110 has as a function the support of an ink jet medium 130 to which suction is applied, through an infinite number of holes formed in the platen 110, to prevent the ink jet medium 130 from floating and to ensure that an appropriate distance is maintained between the ink jet head 100 and the ink jet medium 130.
Further, a capping unit 120 and a wiping unit 121 are provided at the end of the platen 110. The capping unit 120 includes a cap 122 for closing the ink jet head 100 to prevent the ink jet head 100 from drying and to suck up excess ink. As shown in FIG. 3, the capping unit 120 is held by cap springs 200, made of a flexible material, in order to obtain a contact force to be exerted between the cap 122 and the ink jet head 100, and stabilization of the contact force is aimed at by using flexible strokes of the cap springs 200. A cap holding mechanism employing the cap springs 200 is characterized in that the function can be maintained even when the distances between the cap 122 and the ink jet head 100 in the main scanning direction and in the direction perpendicular to the sub-scanning direction, and component parallelism are more or less varied. Furthermore, as another advantage, this mechanism has a simple and stable, low cost structure.
The wiping unit 121 has a wiper 123 for removing foreign substances and ink droplets attached to the ink jet head 100. When the function of the capping unit 120 and the function of the wiping unit 121 are employed together, the cleaning of the ink jet head 100 and the prevention of clogging, and stable printing are provided by a printer.
The ink jet medium 130 is sequentially conveyed across the platen 110 by the rotation of a convey roller 111 and of a nip roller 112, and is moved to an image forming location, while traveling facing the ink jet head 100. The convey roller 111 has a parameter that determines an appropriate feeding distance in accordance with the operating mode of the ink jet printer or the type of ink jet medium 130, and is rotated so as to consistently obtain an image quality. The nip roller 112 is used to press the ink jet medium 130 against the convey roller 111 with an appropriate force so that the convey roller 111 can convey the ink jet medium 130. Some ink jet printers can vary the pressing force applied in accordance with the type of ink jet medium 130. Further, a heater may be prepared for the platen 110 to accelerate the drying of ink ejected onto the ink jet medium 130.
Moreover, at present, there is an ink jet printer having a function that can vary the height of the ink jet head 100 or the carriage 101 to cope with a variety of ink jet media 130. The conventional ink jet media 130 are mainly paper, and the thicknesses range from about several tens to several hundreds of microns; however, currently, a wide range of material is being employed, such as paper, films, cloth and boards, and the thickness range for ink jet media 130 may extend to several millimeters or several of tens of millimeters. A proposal has been put forward for the production of a printer that, while taking the current situation into account, can adjust the height of a maintenance unit by employing head height information (see, for example, Japanese Patent Unexamined Publication No. 2002-361881).
Since the capping unit 120 contacts the ink jet head 100 and tightly closes the nozzle opening of the ink jet head 100 and draws in ink using suction, distances between the ink jet head 100 and the cap 122 in the direction perpendicular to the main scanning direction and in the sub-scanning direction should be appropriately maintained. Otherwise, the function of the capping unit 120 will not be maintained, and not only will the image quality be deteriorated, but also the ink jet head 100 will be damaged, and in some cases, a mechanical function fault may disable an ink jet printer. Therefore, the distance between the ink jet head 100 and the cap 122 is a very important factor in the function maintenance of an ink jet printer. Thus, conventionally, parts are specially employed to adjust the distances between the ink jet head 100 and the capping unit 120, which holds the cap 122, in the direction perpendicular to the main scanning direction and the sub-scanning direction, or the highly accurate machining of parts is employed to obtain predetermined distances between the ink jet head 100 and the capping unit 120 in the direction perpendicular to the main scanning direction and the sub-scanning direction. However, the use of special parts for the adjustment operation and the provision of very accurately machined parts contribute to increases in manufacturing costs. Further, for an ink jet printer that includes multiple ink jet heads 100, the number of sets of ink jet heads 100 and caps 122 that must be adjusted is increased, and a satisfactory contact force must be obtained for all the sets. In addition, when multiple sets of ink jet heads 100 and caps 122 are employed, the inclinations and the parallelism of the ink jet heads 100 and the caps 122 greatly affect the contact force exerted between the ink jet heads 100 and the caps 122. To resolve these problems, the use of very accurately machined parts can not be avoided. Moreover, conventionally, the thickness range of ink jet media 130 is not greatly extended, and ink jet printers are designed on the assumption that for an ink jet head 100 a constant height is adequate. However, recently, as the variety of ink jet media 130 available has increased, a new function for varying the height of an ink jet head 100 is beginning to be added to ink jet printers to permit them to cope with a variety of ink jet media 130 thicknesses. But although this function is being added, the attainment of an adequate capping unit 120 function is difficult for a conventional design based on an ink jet head 100 having a constant height. A mechanism, however, as described in Japanese Patent Unexamined Publication No. 2002-361881, has been proposed that changes the height of a capping unit or a wiping unit, and meshes with the changing of the height of an ink jet head.